Permanent yellow imaged light modulating film

ABSTRACT

This invention relates to the preparation of a supported modulating film having a permanent yellow imaged layer of the homopolymer of a crystalline diacetylene cinnamate monomer ##STR1## and to the use of said film as a light modulator in the production of master printing plates or printed circuit boards.

In one aspect the invention relates to a permanent yellow imagedmodulating or printing plate master film for improved negative imagetransfer by energy generated from a blue light source to a imagereceiving photoresist having a coating which is sensitive to blue light.In another aspect the invention relates to the preparation of saidmodulating film by a non-chemical process.

BACKGROUND OF THE INVENTION

Of the various light sources suitable for photoimaging including red,green and blue, blue light is the most economical and efficient. Ingeneral, the process of preparing a master printing plate having aphotoresist layer involves passing energy from a light source throughnon-imaged portions of a modulator, e.g. a film imaged in a color whichabsorbs the transmitted light and transmits light radiation passingthrough non-imaged areas to the printing plate coated with a materialwhich is imageable in discrete exposed areas upon exposure to radiantenergy. Because of the ready availability and economy of blue lightenergy sources and the numerous films which are sensitive to blue light,extensive research has been directed to finding compounds which areimageable to a permanent yellow hue since such imaged compounds mostefficiently absorb blue light and provide the highest duplicatingproperties. A yellow imaged modulating film would be capable oftransferring energy from its non-imaged areas in a negativeconfiguration of its pattern to a printing plate having a photoresistlayer whereupon the photoresist layer develops color, is polymerized ordepolymerized in the negative pattern dictated by the modulating film inthe highest degree of acuity. Accordingly, a negative or positive of thedesired image can be developed on the printing plate depending upon theyellow pattern or design inscribed on the modulating or master film.

Polyacetylenic compounds have enjoyed great popularity in imagingprocesses. However, it is well recognized that thermochromic behavior ofpolyacetylenic compounds is unpredictable and has been found only incertain narrow classes of this species. Further, within these classes,formation of a permanent yellow hue is extremely rare.

While a few polyacetylenic monomers are capable of providing a yellowimage at excessively high temperatures, this thermochromic effect isephemeral, so that upon cooling, the image reverts to an initialtransition color of darker shades e.g. red, blue, bronze, etc. (U.S.Pat. No. 3,501,303). Such color reversible compounds are useful astemperature or time-temperature indicators dependent on thermal changesbut are not practical for use as modulating films in the preparation ofprinting plates, circuit boards and the like.

Accordingly, it is an object of this invention to provide a permanentyellow imaged film for use as a reverse image transmitting agent ormaster film in the production of printing plates and circuit boards.

Another object is to provide a commercially acceptable and economicalchemically processless method for preparation of a permanent yellowimaged film.

Another object is to provide a commercially acceptable and economicalprocess for using a permanent yellow imaged recording film as a masterfilm in the production of printed circuit boards or master printingplates.

These and other objects of the invention will become apparent from thefollowing description and disclosure.

THE INVENTION

In accordance with this invention there is provided a process whichcomprises exposing a supported layer of colorless, crystallinepolyacetylene cinnamate monomer having the formula ##STR2## to shortwavelength radiation in order to polymerize the monomer to a magentacolored homopolymer and subjecting the resulting homopolymer layer toradiation at a longer wavelength from laser emissions, preferablyfocused to impinge discrete areas of the homopolymer in a predeterminedpattern or design so as to form a permanent yellow image thereon. Thelaser operating at the longer wavelength is one having sufficient beampower to directly or indirectly generate heat of at least 50° C.,preferably between about 50° and about 150° C., in the exposed portionsof the homopolymer. Laser emissions in a wavelength of 575 nm or lessare directly absorbed by the homopolymer. However, the emissions oflasers generating energy in wavelengths above 575 nm are not absorbed;accordingly, in these cases an energy absorbing, heat transmitting agentis employed in conjunction with the diacetylene cinnamate monomer in thepreparation of the initial film before coating on a substrate.

The colorless crystalline diacetylene cinnamate monomer employed hereinis prepared by the transesterification of trans-methyl cinnamate with2-(propargyl) ethanol to form 2-(propargyl) ethyl cinnamate. Theacetylenic cinnamate ester in an inert solvent is then reacted byoxidative coupling with oxygen at a temperature of about 40-45° C. inthe presence of cuprous chloride in the presence of a tertiary amine,e.g. tetramethyl ethylene diamine, as a catalyst.

The resulting diacetylene cinnamate monomer product is recovered byprecipitation, washing with aqueous HCl and water and crystallizationwhereupon it is suitable for use as or in a coating composition appliedto a substrate. The monomer is applied to the substrate in a coatingthickness of from about 0.002 to 100 um, preferably from about 0.01 toabout 5 um. Suitable substrates include polyethylene terephthalate,nylon, polystyrene, cellulose acetate, cellulose nitrate, cellophane,polyvinyl chloride, polyvinylidene chloride, teflon,polychlorotrifluoroethylene, polypropylene, paper, ceramic, glass,metal, wood and the like, however, for use as a modulating film, atransparent substrate is recommended.

Coatings of the present diacetylene cinnamate monomer in the presence orabsence of an energy absorbing, heat transmitting agent, are applied toa substrate by any of the known techniques, including applications ofcrystalline dispersions or of one or more monomolecular layers; however,an aqueous dispersion of crystals fixed with any of the known binders ispreferred. One or more monomolecular layers of the diacetylene cinnamatecompound applied to the substrate by the Langmuir-Blodgett technique,spin or spray coating method is also suitable. Any energy absorbing,heat transmitting agent, which in certain situations may be required,can be applied as a separate, contiguous layer. The preparation ofuseful binder dispersions and coating techniques are more particularlydescribed in my copending U.S. patent application, Ser. No. 07/601,499*,now U.S. Pat. No. 5,095,134. By way of illustration, a dispersion,emulsion or suspension of the crystalline polyacetylenecinnamate/binder, preferably an aqueous dispersion with a binder, isprepared under atmospheric conditions by mixing the crystallinediacetylene cinnamate crystals in a binder solution optionallycontaining an energy absorbing, heat transmitting agent, until auniformly dispersed, suspended or emulsified liquid mixture is obtained.The mixture is then processed by known procedures e.g. chilled or frozenby the process described in U.S. Pat. No. 4,784,934 to provide adispersion of microcrystals in a binder. The diacetylene cinnamatecrystals have a diameter of from about 0.02 um to about 5 um, preferablyfrom 0.1 um to 1.0 um, and are fixed in the binder to provide a uniformdispersion containing from about 1 to about 50 wt %, preferably fromabout 4 to about 15 wt. % of solid microcrystals. This dispersion isthen coated on a substrate and dried to form a layer of between about0.3 to about 10, preferably 0.5 to 5 um thickness. Monomolecular layersof the diacetylene cinnamate are, of course, much thinner; however aplurality of monomolecular layers as well as one or more layers of theenergy absorbing component, when needed, can be sequentially applied toany thickness desired.

The resulting dried diacetylene cinnamate film is then imaged by theprocess of this invention which comprises, in a first stage of apreferred two stage process, exposing the film, at ambient temperatureand pressure to short wavelength radiation; i.e. at a wavelength ofbetween about 200 and about 350 nm, to instantly polymerize thediacetylene cinnamate to a magenta colored homopolymer. Short wavelengthexposure is effected by conventional techniques using a xenon flashlamp, mercury arc lamp, mercury xenon arc lamp, tungsten quartz halogenlamp, electron beam, UV light, actinic light, gamma-rays, X-rays,beta-rays, neutrons, alpha-particles, or UV laser, e.g. an argon ionlaser transmitting energy at about 275 nm wavelength, a krypton ionlaser, a GaAlP laser and the like. The short wavelength exposure can beemployed to homopolymerize all or a portion of the diacetylene cinnamatefilm, that is a broad beam of UV light can be used to homopolymerize theentire colorless diacetylene cinnamate layer (case a) or the layer canbe scribed in one or several steps to define a predetermined pattern orimage with a short wavelength transmitting device e.g. a UV laser orelectron beam operated in the writing mode, (case b). In case (a), theentire film acquires the magenta color of the homopolymer; whereas incase (b) a homopolymerized magenta image is inscribed on the colorlessbackground of the unexposed diacetylene cinnamate. The UV laser which isemployed in case (a) and/or case (b) has an output power of betweenabout 1 mW and about 100 W with an effective dwell time of from about0.01 second to about 5 minutes. Exposure with an electron beam iscarried out under vacuum of from about 10⁻³ to about 10⁻⁹ torr,preferably from about 10⁻⁵ to about 10⁻⁸ torr, using a beam diameter offrom about 0.1 to about 25 μ m, an energy of from about 10 to about 30KeV, and a current flow of from about 10⁻⁹ to about 10⁻⁶ amps. The beamis adapted to scan the target area at a fast rate, e.g. a dwell time ofbetween about 10⁻³ and about 10⁻⁸ second. UV light exposure with awavelength up to about 385 nm, e.g. 200-350 nm, an intensity of fromabout 1 mW to about 100 W for a dwell time of from about 0.1 second toabout 10 minutes is also effective for polymerizing the polyacetylenecinnamate monomer to produce the magenta colored homopolymer. Equivalentdosages are employed for alternate sources of short wavelengthexposures.

The resulting film is then subjected to a radiation source with energyemissions at a longer wavelength above 350 nm in the second stage of thereaction. The radiation source employed, preferably a laser source, iscapable of generating heat sufficient to raise the temperature of thehomopolymer in the exposed areas to between about 50° and about 150° C.,preferably between about 60° and about 80° C., thus causing a permanentcolor change from magenta to yellow in the areas impinged by the laseremission in the second stage. In case (a) above, the laser source isemployed in the writing mode to inscribe a predetermined permanentyellow image on the magenta colored homopolymer layer. In case (b)above, the laser source operating at the longer wavelength can besynchronized with the scribing device operating at the short wavelengthand used in the writing mode to retrace a previously inscribed image orit can be used to expose the entire polymerized and non-polymerizedportions of the diacetylene cinnamate layer so as to transmit apermanent yellow color to induce a chromic change to a permanent yellowcolor in the preinscribed magenta image. This operation is carried outunder ambient pressure for a period sufficient to complete the colortransition, which time period is dependent upon the laser beam power andtype of laser imaging device selected The second stage heat generationcan be supplied by substantially any laser generating energy in the 450nm or longer wavelength regions of the spectrum. Such lasers include acompact semi-conductor diode, solid state, gas, metal vapor, or dyelaser. However, semi-conductor diode lasers, having an output power offrom about 1 microwatt to about 10 watts, are preferred. Specificexamples of suitable lasers include GaAlAs, NaYtAl garnet, Ar, He-Ne,He-Cd, GaAs NeYAl garnet, ruby, NaYAg, krypton ion, copper vapor lasers,etc. Thus, crystalline, gas or amorphous solid, pulsed or continuouswave lasers may be used. For scribing, a laser beam diameter of 0.5 toabout 2 nm with an exposure time of from about 180 to 250 ns/dot and anoutput of 2.5-3.5 mW is generally employed to create an image of highresolution.

The laser source selected should be capable of transmitting the desiredheat needed to induce the chromic color change in the laser exposedareas of the homopolymerized diacetylene cinnamate layer at betweenabout 350 and about 580 nm wavelength, which is within the absorptioncapability of the homopolymer. Alternatively, a laser transmittingenergy at a higher wavelength, for example above about 350 up to about1500 nm or higher can be employed, provided that a suitable energyabsorbing, heat transmitting component, such as an energy absorbingpolycarbocyanine dye, pyrylium dye, squarilium dye or a dye mixture oran intermixture as described in greater detail in copending U.S. patentapplication Ser. No. 07/601,537*, is used in conjunction with thediacetylene cinnamate to absorb energy from the laser and to transmitsufficient heat to the polymer so that a yellow image or pattern isinscribed thereon. The energy absorbing, heat transmitting agent is onehaving absorption capability in a wavelength similar to the transmittinglaser and is capable of raising the temperature of the homopolymer to atleast 50° C. When an energy absorbing dye is employed, the weight ratioof diacetylene cinnamate polymer to dye can vary between about 1000:andabout 1:10, depending upon the amount of homopolymer present and theamount of radiation energy needed to be converted to heat energy. Mostoften the dye comprises between about 0.005 and about 10 wt. % of theimaging compound.

In another embodiment of this invention, dual laser exposures can beeffected with a single laser unit wherein a short in advance of a longwavelength energy generating laser is mounted. Because of the time lagin generating heat, as opposed to instantaneous polymerization, thelaser emissions from the two beams, in synchronized phase, may befocused to impinge simultaneously on each pixel of the imageable layerfor direct recording of a yellow image.

The resulting permanent yellow imaged film product supported on atransparent substrate can then be employed as a master film in thepreparation of a printing plate or etch resist coated with a layer whichis photosensitive to blue light transmission.

The image receptive device, e.g. an etch resist for a printed circuitboard, a master printing plate, etc. can be composed of any durablesupport material such as metal, glass, ceramic, polyester, and the likewhich is coated with a photosensitive layer, comprised of any knownphotosensitive materials which undergo polymerization or a thermochromicchange in response to radiation from a blue light source. Of thesematerials, colorless, thermochromic conjugated polyacetylenic monomers,their monomeric derivatives, diazo resins, cinnamic ester resins,polymethacrylates or a silver halide based film are suitable; however,crystalline, imageable diacetylene derivatives are preferred. Examplesof preferred diacetylenic compounds comprising the photosensitivesurface layer of the image receiving device include any of the artrecognized hydrocarbon diacetylenes, and their derivatives such as thecarboxyl, amino, amido, ester, ether, urea or carbamate substituteddiacetylenes as well as tri- and tetra- acetylene derivatives of thesespecies.

The homopolymerized diacetylene cinnamate of the present invention hasother uses in addition to photoimaging. For example this homopolymer isuseful as time-temperature or temperature indicator coatings as warmingmeans for equipment which is subject to overheating. However, thephotoimaging application of the homopolymer is emphasized since thisproduct possesses unusual properties such as a permanent yellowthermochromic imaging and non-chemical development to images of superiorresolution and intensity, which are so important in the photographicarts.

Having generally described the invention, reference is now had to theaccompanying examples which are presented to illustrate preferredembodiments but which are not to be considered as limiting to the scopeof this invention as is more broadly described above and in the appendedclaims.

EXAMPLE A. Preparation of [C₆ H₅ CH═CH--COOC₂ H₄ OCH₂ C.tbd.C--₂ ]

Trans methyl cinnamate (324.4 g, 2 moles), 2-(propargyloxy) ethanol(200.1 g) and concentrated sulfuric acid (1 ml) were charged into aone-liter flask equipped with a mechanical stirrer, a thermometer, anitrogen inlet and an adapter connected to a condenser. The solution washeld at 110° C. over night under a flowing stream of nitrogen to removemethanol by-product. The remaining liquid was then vacuum distilled anda center cut of 280.7 g was collected at 147° C. and 0.01 mm Hg. The2-(propargyloxy) ethanol product in 98% purity was recovered andidentified by Ir and nmr analysis.

2-(Propargyloxy) ethanol (78.1 g), tetrahydrofuran (340 ml), tetramethylethylene diamine (20 g) and cuperous chloride (3 g) were charged into aone-liter flask. A stream of oxygen was bubbling through the solutionwith vigorous stirring for 11 hours at 40-45° C. The tetrahydrofuransolvent was then stripped off. The crude product was washed two timeswith 300 ml of 10% HCl solution and two times with water. After beingdried in air, 72.5 g of 2-(propargyloxy) ethyl cinnamate, m.p. 47-50° C.was obtained. The structure of the chemical was identified by nmr and IRanalyses.

B. Preparation of Coating Dispersion

In a glass container, 1.2 g. of the above product were dissolved atabout 50° C. in 3.6 g. of ethyl acetate and the resulting solution wasfiltered and designated Solution A. A second solution, designatedSolution B, was prepared by dissolving 1.2 g. of photographic gelatinand 0.05 g. of ALKANOL XC (an alcohol-containing wetting agent, suppliedby E.I. duPont) in 30 g. of water. Solution B was heated to 60° C. andintroduced into a 250 ml Waring Blender. While blending at high speed,Solution A was added to Solution B after which the blending wascontinued for 2 minutes. The resulting mixture was then poured into acrystallizing dish to chill set at about 12° C. The resulting gelleddispersion was then cut into approximately 1 cm cubes and allowed towarm in an air stream at approximately 32° C. to remove ethyl acetate byevaporation. After the ethyl acetate had been removed the gelleddispersion was reconstituted by melting at 40° C. and adding sufficientwater to replace the weight loss that occurred during drying.

C. Coating a Film Base with Dispersion

The reconstituted dispersion was coated at about 8 micrometers thicknesson a poly(ethylene terephthalate) film base which had been overcoatedwith a 1 micrometer thick layer of an adhesion promoting materialcomposed of about 50 wt. % gelatin and 50 wt. % of a latex polymer. Thecoated film was then allowed to dry in air at ambient temperature.

D. Imaging the Film

A 4 ×4 inch sample of the above film was placed in a holding device overwhich is mounted a low pressure mercury arc lamp having a 100 wattoutput and emitting UV radiation at a maximum wavelength of about 253.7nm. The colorless film is exposed for 0.second to emissions from thelamp so as to absorb energy and polymerize colorless [C₆ H₅ --CH═CHCOOC₂H₄ OCH₂ C.tbd.C--₂ --]to a rich magenta homopolymer.

The resulting homopolymer is then scribed with a copper vapor laserhaving an output of 3 watts which transmits energy at about 560 nmwavelength and impinges discrete areas of the surface of the filmdefined by a series of diamond shaped figures and lines. The energygenerated by this transmission is absorbed by the homopolymer and heatsthe exposed areas of the film to a temperature of about 65° C. in afraction of a second whereby an image of said diamond shaped figures andlines is transmitted in high acuity in a permanent bright yellow coloron the magenta background which is not exposed to the laser emissions.

E. Use of the Yellow Imaged Film as a Modulating Film

The above sample is employed as a modulating film in the following test.A blue light source, i.e. a high pressure mercury arc lamp operating atan output power of 1 kilowatt and transmitting energy in a wavelength of350-450 nm is focused to scan the entire area of the film sample whichis positioned about 3.6 feet from the light outlet. Contiguous with thesurface of the film and on the surface directly opposite the surfacebeing radiated, is positioned the imageable surface layer, i.e.4-diazodiphenyl-amine/formaldehyde condensate, supported on cellulosetriacetate sheet of the photoresist master printing plate.

The blue light from the lamp is absorbed in the imaged areas of the filmsample and is transmitted from the non-imaged areas, in an exactnegative imaged pattern to the imageable surface layer of thephotoresist where it attacks the polymer condensate and renders thedecomposed areas insoluble in water.

EXAMPLE 2

Example 1 is repeated except that in Part B, 0.1 wt. % of IR-125 dye (apolycarbocyanine dye supplied by Eastman Kodak) is added to solution Band a GaAlAs semiconductor diode laser with a wavelength of about 830 nmis substituted for the copper vapor laser in Part D. The image producedis one of high resolution defined in a bright yellow color on a magentacolored background.

EXAMPLE 3

Example 1 is repeated except that in part D, an electron beam writingdevice is used in place of the high pressure mercury arc lamp. Theelectron beam is used to instantly homopolymerize diacetylene and towrite an image consisting of a series of lines by homopolymerizing thediacetylene cinnamate monomer in the corresponding discrete areas ofexposure. The image is instantly visible as magenta lines on a colorlessnon-exposed monomer background. After about 1 hour, in the same manner,dots between the magenta lines are inscribed on the film with theelectron beam scriber to provide a magenta image of lines and dots onthe unexposed colorless background. Also in Part D, a broad exposure ofthe entire film is made with the copper vapor laser instead of impingingdiscrete areas. Within a fraction of a second the well defined image ofthe magenta lines and dots is transformed to a permanent bright yellowimage.

It is to be understood that many modifications and substitutions can bemade in the above examples without departing from the scope of thisinvention. For example, any of the other radiation devices whichtransmit energy in a short wavelength of 200-350 nm and/or any of thelasers which transmit energy in the longer wavelength above 350 nm canbe substituted in the above examples in accordance with the teachings ofthis invention. Also any of the energy absorbing heat transmitting dyesincluding other polycarbocyamine dyes, squarilium or pyrilium dyes anddye complexes mentioned or described in copending U.S. patentapplication, Ser. No. 601,32, filed concurrently herewith, and in U.S.Pat. No. 4,513,071 which absorb energy in a wavelength similar to thatof the energy generated from the laser can be substituted in the aboveexamples or examples indicated by the above substitutions. Additionally,substitutions of other base films in Parts C and Parts E of the aboveexamples or substituted examples, as well as other photoresist coatingsfor the image receiving device in Parts E can be made without departingfrom the scope of this invention.

What is claimed is:
 1. The permanently and directly yellow-imageablecomposition containing the homopolymer of the diacetylene cinnamatehaving the formula [C₆ H₅ --CH═CH--CO--PCH₂ CH₂ OCH₂ --C.tbd.C--₂ --]and between about 0.001 and about 10 wt. % of an energy absorbing, heattransferring agent having absorption in the wavelength range of fromabout 57 and about 1,500 nm.
 2. The composition of claim 1 wherein saidagent contains a polycarbocyanine dye as an active energy absorbingagent.
 3. The composition of claim 1 wherein said agent contains asquarilium dye as an active energy absorbing agent.